NdFeB magnet containing cerium and manufacturing method thereof

Abstract

A NdFeB magnet containing cerium and a manufacturing method thereof are provided. The manufacturing method includes steps of: refining a part of raw materials pure iron, ferro-boron, and rare earth fluoride in a crucible, adding a rest of the raw materials into the crucible and refining, casting a refined solution to a surface of a water-cooled rotation roller through a tundish and forming alloy flakes, processing the alloy flakes containing at least two different compositions with hydrogen decrepitation, milling powders, magnetic field pressing, vacuum presintering, machining and sintering, and obtaining the NdFeB magnet containing cerium. The NdFeB magnet containing cerium has a density of 7.5-7.7 g/cm.sup.3 and an average particle size of 3-7 m; comprises a main phase and a grain boundary phase distributed around the main phase. A composite phase containing Tb is provided between the main phase and the grain boundary phase.

Claims

1. A method for manufacturing a NdFeB magnet containing cerium, comprising steps of: (a) sending a portion of raw materials, comprising pure iron, ferro-boron, and rare earth fluoride, into a crucible of a vacuum melting chamber under a vacuum condition, heating the portion of raw materials to a temperature of 1400-1500 C., and then refining the portion of raw materials; (b) sending a rest of raw materials comprising the rare earth into the crucible of the vacuum melting chamber, injecting argon gas into the vacuum melting chamber, refining the raw materials in the crucible; casting a molten solution after refining to a surface of a water-cooled rotation roller through a tundish, and forming alloy flakes; (c) sending at least two kinds of alloy flakes with different compositions into a hydrogen decrepitation furnace, and processing with a hydrogen decrepitation process; wherein: at least one kind of alloy flakes is prepared through the steps (a)-(b); (d) sending the alloy flakes after the hydrogen decrepitation process into a nitrogen jet mill, and then milling the alloy flakes into powders by the nitrogen jet mill; (e) under a protection of nitrogen, processing the powders with magnetic field pressing, and obtaining a pressed compact; (f) under the protection of the nitrogen, sending the pressed compact into a vacuum sintering furnace, vacuum presintering the pressed compact, and obtaining a presintered block; (g) machining the presintered block into a part; and (h) processing the part with vacuum sintering and aging, and obtaining the NdFeB magnet containing cerium, wherein: a vacuum sintering temperature is controlled in a range of 960-1070 C., an aging temperature is controlled in a range of 460-640 C., a density of the NdFeB magnet containing cerium is 7.5-7.7 g/cm.sup.3, the average grain size is in the range of 3-7 m, the NdFeB magnet containing cerium comprises the main phase and the grain boundary phase distributed around the main phase, the main phase contains rare earth elements and contains at least La, Ce, Pr and Nd, the grain boundary phase contains Ce, N and F, the total weight percentage of La and Ce in the rare earth of the NdFeB magnet containing cerium is 1-69%, and the contents of N and F in the NdFeB magnet containing cerium are respectively 0.021 wt %N0.09 wt % and 0.004 wt %F0.5 wt %.

2. The method for manufacturing the NdFeB magnet containing cerium, as recited in claim 1, wherein: the rare earth fluoride comprises at least one member selected from the group consisting of lanthanum fluoride, cerium fluoride, neodymium praseodymium fluoride, terbium fluoride, and dysprosium fluoride.

3. The method for manufacturing the NdFeB magnet containing cerium, as recited in claim 1, wherein: in the step (b), the rest of raw materials further comprises NdFeB scraps; a weight of the NdFeB scraps is 10-60% of a total weight of the raw materials; and a weight of the rare earth fluoride is 0.1-6% of the total weight of the raw materials.

4. The method for manufacturing the NdFeB magnet containing cerium, as recited in claim 1, wherein: in the step (a), a vacuum degree is controlled in a range of 810.sup.1-810.sup.2 Pa; and a content of Mn in the NdFeB magnet containing cerium is controlled in a range of 0.011-0.046 wt %.

5. The method for manufacturing the NdFeB magnet containing cerium, as recited in claim 1, wherein: the hydrogen decrepitation process comprises steps of: firstly adding terbium fluoride powders into the alloy flakes; then heating the alloy flakes to a temperature of 120-800 C., and keeping the temperature for 10 minutes to 8 hours; cooling the alloy flakes to 100-390 C.; absorbing hydrogen; heating the alloy flakes to a temperature of 600-900 C. and keeping the temperature; and cooling the alloy flakes to below 200 C. in sequence; the content of F in the NdFeB magnet containing cerium is in a range of 0.005-0.5 wt %; and a content of Tb in the NdFeB magnet containing cerium is in a range of 0.1-2.9 wt %.

6. The method for manufacturing the NdFeB magnet containing cerium, as recited in claim 1, wherein: in the step (d), the nitrogen jet mill for milling the alloy flakes into the powders is a nitrogen jet mill without discharging ultrafine powders; the powders prepared through the nitrogen jet mill comprise ultrafine powders having a particle size smaller than 1 m and powders having a particle size larger than 1 m, and the ultrafine powders have a higher nitrogen content and a higher heavy rare earth element content than the powders having the particle size larger than 1 m; after uniformly mixing the ultrafine powders and the powders having the particle size larger than 1 m, the ultrafine powders surround the powders having the particle size larger than 1 m.

7. The method for manufacturing the NdFeB magnet containing cerium, as recited in claim 1, wherein: before milling the alloy flakes into powders by the nitrogen jet mill in the step (d), the step (d) further comprises adding a lubricating agent into the alloy flakes after the hydrogen decrepitation process; and the lubricating agent contains F.

8. The method for manufacturing the NdFeB magnet containing cerium, as recited in claim 1, wherein: in the step (f), the pressed compact is vacuum presintered and the presintered block is obtained, a density of the presintered block is controlled in a range of 5.1-7.4 g/cm.sup.3; in the step (g), the presintered block is machined and the part is obtained, powders or a film containing Tb is attached to a surface of the part; in the step (h), the part attached with the powders or the film containing Tb on the surface thereof is sent into the vacuum sintering furnace, and processed with vacuum sintering and aging, the NdFeB magnet containing cerium is obtained, the vacuum sintering temperature is controlled in the range of 1010-1045 C., the aging temperature is controlled in the range of 460-540 C., the density of the NdFeB magnet containing cerium is 7.5-7.7 g/cm.sup.3, the average grain size is in the range of 3-6 m, a content of Tb in the NdFeB magnet containing cerium is in a range of 0.1-2.9 wt %.

9. The method for manufacturing the NdFeB magnet containing cerium, as recited in claim 8, wherein: after machining the presintered block and obtaining the part, the powders containing Tb are attached to the surface of the part through a pressure immersing method, or the film containing Tb are attached to the surface of the part through at least one of sputtering, evaporating and spraying method, and then the part attached with the powders containing Tb on the surface thereof or the part attached with the film containing Tb on the surface thereof is sent to the vacuum sintering furnace, and processed with vacuum sintering and aging.

10. The method for manufacturing the NdFeB magnet containing cerium, as recited in claim 1, wherein: in the step (f), the pressed compact is vacuum presintered and the presintered block is obtained, a density of the presintered block is controlled in a range of 5.1-7.2 g/cm.sup.3; in the step (g), the presintered block is machined and the part is obtained, the part is immersed into a solution containing TbAl alloy powders; in the step (h), the part containing TbAl alloy powders is sent into the vacuum sintering furnace, and processed with vacuum sintering and aging, the NdFeB magnet containing cerium is obtained, the vacuum sintering temperature is controlled in the range of 1010-1045 C., the aging temperature is controlled in the range of 460-540 C., the density of the NdFeB magnet containing cerium is 7.5-7.7 g/cm.sup.3, a content of Tb in the NdFeB magnet containing cerium is in a range of 0.1-2.9 wt %; the grain boundary phase contains F, a composite phase containing Tb and N is provided between the main phase and the grain boundary phase, the composite phase has a structure of (R, Tb).sub.2T.sub.14(B, N), T represents transition metal elements and contains Fe, Mn and Co, and R represents at least one rare earth element and contains Pr or Nd.

11. The method for manufacturing the NdFeB magnet containing cerium, as recited in claim 1, wherein: in the step (f), the pressed compact is vacuum presintered and the presintered block is obtained, a density of the presintered block is controlled in a range of 5.1-7.2 g/cm.sup.3; in the step (g), the presintered block is machined and the part is obtained, the part is immersed into a solution containing terbium fluoride powders; in the step (h), the part containing terbium fluoride powders is sent into the vacuum sintering furnace, and processed with vacuum sintering and aging, the NdFeB magnet containing cerium is obtained, the vacuum sintering temperature is controlled in the range of 1010-1045 C., the aging temperature is controlled in the range of 460-540 C., the density of the NdFeB magnet containing cerium is 7.5-7.7 g/cm.sup.3, the content of F in the NdFeB magnet containing cerium is in the range of 0.05-0.5 wt %, and a content of Tb in the NdFeB magnet containing cerium is in a range of 0.1-2.9 wt %.

Description

EXAMPLE 1

(1) An alloy raw material, which is made into alloy flakes Al containing Ce, is prepared by raw materials praseodymium neodymium alloy, cerium fluoride, pure iron, ferro-boron, metallic gallium, metallic zirconium, metallic cobalt, metallic aluminum, and metallic copper; the pure iron, ferro-boron, the cerium fluoride and a small amount of the praseodymium neodymium alloy are put into a first charging basket, a rest of the praseodymium neodymium alloy and the metallic gallium are put into a second charging basket, the metallic zirconium, the metallic cobalt, the metallic aluminum, and the metallic copper are put into a third charging basket; and then the first charging basket, the second charging basket and the third charging basket are sent into a vacuum loading chamber of a vacuum melting rapid-solidifying device; after being vacuumized, a vacuum valve between the vacuum loading chamber and a vacuum melting chamber is opened; through a cooperation among a lifting device, a multistage rotation plate, and a trolley which moves back and forth, the raw materials in the first charging basket are sent to a crucible of the vacuum melting chamber under a vacuum condition, heated to 1400-1500 C., and refined; the raw materials in the second charging basket and the third charging basket are also sent to the crucible of the vacuum melting chamber, and then argon gas is injected into the crucible and the raw materials are refined, wherein: during the refining process, a vacuum degree is controlled to be in a range of 810.sup.1 Pa to 810.sup.2 Pa, vacuum demanganizing is performed; after the refining process, a molten solution is cast to a surface of a water-cooled rotation roller by tilting the crucible through a tundish, alloy flakes are formed; after leaving the water-cooled rotation roller, the alloy flakes fall into an alloy flake crushing device in an alloy flake cooling chamber, the crushed alloy flakes fall into a water-cooled rotation cylinder and secondarily cooled, the alloy flakes Al are prepared; mixed alloy flakes having a composition of (Pr.sub.0.25Nd.sub.0.75).sub.20.1Ce.sub.10Fe.sub.residualCo.sub.0.8Al.sub.0.1B.sub.0.95 Cu.sub.0.1Ga.sub.0.1Zr.sub.0.14 are prepared by the alloy flakes Al and other alloy flakes A2 without Ce, sent into a vacuum hydrogen decrepitation furnace and processed by hydrogen decrepitation, wherein: while hydrogen decrepitation, terbium fluoride powders are added to the mixed alloy flakes, and then heated to 650 C., kept at 650 C. for 2 hours, cooled to 260 C., processed by absorbing hydrogen, heated to 650 C. again and kept at the temperature, and finally cooled to below 200 C. in sequence; after the hydrogen decrepitation process, the mixed alloy flakes are sent into a nitrogen jet mill without discharging ultrafine powders, milled into powders by the nitrogen jet mill, and an average particle size of the powders is controlled at about 2.0-2.2 m; the powders are processed with magnetic field pressing, a pressed compact is obtained, and the pressed compact is presintered into a presintered block with a presintering density of about 5.6 g/cm.sup.3; the presintered block is machined into a part; oil is removed from the part, and then the part is immersed into a solution containing the terbium fluoride powders; the part containing the terbium fluoride powders is sent into a vacuum sintering furnace, the part is processed with vacuum sintering and aging, and a vacuum sintering temperature is controlled at about 1040 C., an aging temperature is controlled at about 505 C., and a density of the part is controlled at 7.4 g/cm.sup.3; and, after subsequent processes, a NdFeB permanent magnet device D1 is obtained. Through detecting, it is found that the NdFeB permanent magnet device D1 has a magnetic energy product of 50 MGOe and a coercive force of 12 kOe. The NdFeB permanent magnet products, in the same batch of the NdFeB permanent magnet device D1, have few broken edges and corners, and a low rejection rate.

(2) Alternatively, it is feasible to machine the presintered block into the part, and then immerse the part into any other solutions containing powders of Tb, or attach powders containing Tb on a surface of the part through a pressure immersing method, or form a film containing Tb on the surface of the part through at least one method of sputtering, evaporating and spraying; next, the part, attached with the powders or the film containing Tb on the surface thereof, is sent into the vacuum sintering furnace and processed with vacuum sintering, aging, and subsequent processes. The obtained permanent magnet device has a similar magnetic performance as the NdFeB permanent magnet device D1. The permanent magnet products, in the same batch of the permanent magnet device D1, have few broken edges and corners, and a low rejection rate.

EXAMPLE 2

(3) An alloy raw material, which is made into alloy flakes A3 containing Ce, is prepared by raw materials praseodymium neodymium alloy, cerium fluoride, dysprosium iron, pure iron, ferro-boron, metallic gallium, metallic zirconium, metallic cobalt, metallic aluminum, and metallic copper; the pure iron, ferro-boron, the cerium fluoride and a small amount of the praseodymium neodymium alloy are put into a first charging basket, a rest of the praseodymium neodymium alloy, the dysprosium iron and the metallic gallium are put into a second charging basket, the metallic zirconium, the metallic cobalt, the metallic aluminum, and the metallic copper are put into a third charging basket; and then the first charging basket, the second charging basket and the third charging basket are sent into a vacuum loading chamber of a vacuum melting rapid-solidifying device; after being vacuumized, a vacuum valve between the vacuum loading chamber and a vacuum melting chamber is opened; through a cooperation among a lifting device, a multistage rotation plate, and a trolley which moves back and forth, the raw materials in the first charging basket are sent to a crucible of the vacuum melting chamber under a vacuum condition, heated to 1400-1500 C., and refined; the raw materials in the second charging basket and the third charging basket are also sent to the crucible of the vacuum melting chamber, and then argon gas is injected into the crucible and the raw materials are refined, wherein: during the refining process, a vacuum degree is controlled to be in a range of 810.sup.1 Pa to 810.sup.2 Pa, vacuum demanganizing is performed; after the refining process, a molten solution is cast to a surface of a water-cooled rotation roller by tilting the crucible through a tundish, alloy flakes are formed; after leaving the water-cooled rotation roller, the alloy flakes fall into an alloy flake crushing device in an alloy flake cooling chamber, the crushed alloy flakes fall into a water-cooled rotation cylinder and secondarily cooled, the alloy flakes A3 are prepared; mixed alloy flakes having a composition of (Pr.sub.0.25Nd.sub.0.75).sub.15.1Ce.sub.15Dy.sub.0.2Fe.sub.residualCo.sub.0.8Al.sub.0.1B.sub.0.95Cu.sub.0.1Ga.sub.0.1Zr.sub.0.14 are prepared by the alloy flakes A3 and other alloy flakes A4 without Ce, sent into a vacuum hydrogen decrepitation furnace and processed by hydrogen decrepitation, wherein: while hydrogen decrepitation, terbium fluoride powders are added to the mixed alloy flakes, and then heated to 650 C., kept at 650 C. for 2 hours, cooled to 260 C., processed by absorbing hydrogen, heated to 650 C. again and kept at the temperature, and finally cooled to below 200 C. in sequence; after the hydrogen decrepitation process, the mixed alloy flakes are sent into a nitrogen jet mill without discharging ultrafine powders, milled into powders by the nitrogen jet mill, and an average particle size of the powders is controlled at about 2.0-2.2 m; the powders are processed with magnetic field pressing, a pressed compact is obtained, and the pressed compact is presintered into a presintered block with a presintering density of about 5.5 g/cm.sup.3; the presintered block is machined into a part; oil is removed from the part, and then the part is immersed into a solution containing the terbium fluoride powders; the part containing the terbium fluoride powders is sent into a vacuum sintering furnace, the part is processed with vacuum sintering and aging, and a vacuum sintering temperature is controlled at about 1040 C., an aging temperature is controlled at about 505 C., and a density of the part is controlled at 7.3 g/cm.sup.3; and, after subsequent processes, a NdFeB permanent magnet device D2 is obtained. Through detecting, it is found that the NdFeB permanent magnet device D2 has a magnetic energy product of 51 MGOe and a coercive force of 13 kOe. The NdFeB permanent magnet products, in the same batch of the NdFeB permanent magnet device D2, have few broken edges and corners, and a low rejection rate.

(4) Alternatively, it is feasible to machine the presintered block into the part, and then immerse the part into any other solutions containing powders of Tb, or attach powders containing Tb on a surface of the part through a pressure immersing method, or form a film containing Tb on the surface of the part through at least one method of sputtering, evaporating and spraying; next, the part, attached with the powders or the film containing Tb on the surface thereof, is sent into the vacuum sintering furnace and processed with vacuum sintering, aging, and subsequent processes. The obtained permanent magnet device has a similar magnetic performance as the NdFeB permanent magnet device D2. The permanent magnet products, in the same batch of the permanent magnet device D2, have few broken edges and corners, and a low rejection rate.

(5) One skilled in the art will understand that the embodiment of the present invention as shown in the drawings and described above is exemplary only and not intended to be limiting.

(6) It will thus be seen that the objects of the present invention have been fully and effectively accomplished. Its embodiments have been shown and described for the purposes of illustrating the functional and structural principles of the present invention and is subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.